Method of and means for grinding and polishing sprocket teeth



Sept. 6, 1938. E. ROSS 2,129,031

METHOD OF AND MEANS FOR GRINDING AND POLISHING SPROCKET TEETH Filed April 24, 1935 lfllllllll mu INVENTOR Ernest Russ BY ATTOR N EY Patented Sept. 6, 1938 UNITED STATES METHOD OF AND MEANS FOR GRINDING AND POLISHING SPROCKET TEETH Ernest Ross, Elmhurst, Long Island, N. Y., as-

signor to United Research Corporation, Long Island City, N. Y., a corporation of Delaware Application April 24, 1935, Serial No. 17,892

9 Claims.

This invention relates to the manufacture of sprockets and particularly to that phase of their manufacture having to do with the grinding and polishing or lapping of the faces of the teeth which contact the material, such as talking motion picture film, to be driven or moved thereby.

When motion picture film was the medium solely for the recording of pictorial images, it was only necessary to move the film through a recording device, such as the camera, or through a reproducing device, such as the projector, from a supply reel to and from the intermittent motion and to the take-up reel, without mutilation. At present, however, where therecord carrier or film is also utilized for images of sound in the form of a sound record, the sound constituting one or more frequencies of different amplitudes and phase relationships, it-has become extremely important to progress the film at a constant linear velocity past the sound translation point in the recorder and reproducer. This requires not only a constant rotational speed of the sprocket which drives the film past the translation point, but a sprocket which permits this constant rotational 5 speed to be imparted to the-film smoothly and uniformly.

The present invention, therefore, has as its principal object the provision of a sprocket whose teeth are so formed and finished that ingress and egress to and from the perforations of the film is facilitated and abrasion of the film at the point of contact is reduced to a minimum. Heretofore, it has been the practice to grind the sprocket teeth transversely, th t is, at right angles to .the direction 'o'f film over'neiit when I the film leaves the sprocket teeth. The present invention provides a method of grih'dirig and l'apping the teeth in the direction of movement of the film, thus eliminating any transverse ridges and providing a surfacewhich has its tool marks,

if any, in the direction of film movement.

The invention will be more fully understood from the following description read in conjunction with the accompanying drawing in which 5 Figs. 1, 2 and 3 show partial detail sections of a sprocket made in accordance with the invention.

Fig. 4 is a plan view of the grinding and polishing device; and

50 Figs, 5, 6 and 7 are views of details of the device shown in Fig. 4.

Referring to the drawing, a pantograph device 5 includes an adjustable work table 6 for holding the sprockets to be ground and a guide or 55 control table 7. Interconnecting the two tables 6 and l are the pantograph arms l, 2, 3 and 4, arm 4 being adjustably pivoted on an arm ill, the latter being fixedly pivoted on bracket i i. Upon arm t is a tool holder l3'shown in detail in Fig. 7,

and which includes a pulley Mrotatably mounted 5 on a shaft i5 with a hollow tapered portion it for holding a tool such as a grinding tool ll. The holder it may be held in position upon the arm d by means of set screws it and the tool rotated by belt it from a suitable power source. 1 0 Since the action of a pantograph arrangement is well understood in the art, the geometry and operation thereof will not be described, it being understood that any motion at the table l will be reproduced at the work table 6 in a ratio de- 15 pendent upon the positioning of the holder l3 upon the arm t and the connection of the arm 3 to the arm it. Both tables 6 and l are provided with grooves for securing a templet, dividing head, or the material to be worked firmly there- 20 "on, as is well understood in milling machine practice. The table 6 is adjustable in three directions, handles 8 and 9 with their micrometer indicia i2 and 241, respectively, and. cooperating mechanism providing the means for making lon- 25 gltudinal and transverse adjustments while similar means, not shown, are employed for the vertical adjustment.

As shown in Fig. 5, brackets 2d hold the base?! of a dividing or index head to the table 6, this 30 dividing head being provided with a rotatable cylindrical portion 22. Upon the portion 22 is a smaller tapped cylindrical portion 23 upon which one or more sprocket rings 25 are held firmly in position by means of screws 26 and clamp ring 3 H. The sprocket ring is arranged so that a radius ofthe ring passing through its center and the center of the first tooth is perpendicular to one of the lines of transverse travel of thetable ii. Index holes 29 are provided in the portion 22, the 40 number thereof being usually either equal in number to the sprocket teeth or an even multiple thereof. A bracket 3i supports an index pin 32 for firmly positioning the sprocket in each adjusted position, the head 22, as mentioned above, being rotatable on its base H- In Fig. 6 the controlling arm for the grinding tool H is shown in detail and comprises a pivot block 35 which is securely fastened in any suitable manner to the table 1 and upon which is pivoted an arm 36 in which a slot 31 is provided. The arm 36 rotates about a pivot point 39 while pantograph arm i is pivoted at a point 40 on a block H adjustable within the slot 37 by threaded shaft 43 having a hand knob Hi. The block 4| and arm 36 may have Vernier adjustment gradations thereon or micrometer gradations may be placed on the rotational portion 45 attached to shaft 43. This arrangement provides means for varying the radius of curvature for the travel of tool I! as will be explained hereinafter.

A section of a completed sprocket is illustrated in Fig. 3 wherein the tooth ring 25 is mounted between a clamp collar 46 and a shoulder", the ring 25 being held firmly in position between 45 and 41 by a screw 48. It is to be noted that the collar and shoulder upon which the film is supported is beyond the root or throat of the teeth so that only the face portions of the teeth contact the film, as shown in Fig. 2, with a film section 28 shown in position by the dotted lines. The complete sprocket assembly is disclosed and claimed in my co-pending application Serial No. 15,771 filed April 11, 1935.

As mentioned above, the grinding and polishing device just described functions to provide a finished surface which has no ridges or tool marks of any kind transverse or in a direction to interfere with the motion of the film when leaving the sprocket teeth. The ring 25 to be ground is placed on the dividing fixture 22 clamped in position and adjusted as above described. The pantograph arm 2 is then pivoted at 39 and the table 6 adjusted until the tool I! is positioned at the center of the sprocket ring.

Now referring to Fig. 1, a plurality of positions of the grinding tool is illustrated by circles 50 along arcs 5| and 52 having centers 0. and b respectively. The position of centers a and b are dependent upon the size of the sprocket, the pitch and curvature of the teeth. In the final position of the polishing tool, its center will follow the arcs 5| and 52 with centers a and 1).

Assuming that the pantograph 5 is set for a one to one ratio, then the center of tool I! will follow an arc of the same radius as the center of pivot 40, other ratios producing proportionate arcs. When the radius has been determined, this radius is measured between pivot 39 and pivot 40 as f (see Fig. 6) and the position of block 4| noted. Since there is some material to be removed or abraded by grinding and polishing, the:

pivot 40 may be moved back an additional distance g for instance, to adequately clear the tooth.

Now with the pantograph arm I still pivoted at 39 and the axis 'of tool l'l coincident with the axis of the ring 25, the table 6 is lowered to bring the ring 25 below the tool II. The sprocket ring is then positioned laterally by, the handles 8 and 9 until the axis of tool I! corresponds to either center a or b (see Fig. 1) one lateral adjustment from a central position of the ring corresponding to the normal distance between radial line 0 and either parallel line d or. e passing through centers (1. and b respectively. The other lateral adjustment perpendicular to the first adjustment is slightly less than the square root of the square of the radius of the base circle 49 minus the squarev of the lateral distance between e and c or c and d. Either adjustment may be made first. It is to be noted that the radius of arcs 5| and 52 is the radius of the faces of the teeth plus the radius of the tool l1.

When the work is once positioned as just described, the table 6 is raised to bring the ring and tool in working relationship and the block 4| moved towardthe pivot 39 until the tool l1 touches the face of a tooth. The arm 36 is now oscillatedback and forth in a direction dependanarc depending upon the position of the ringon the table 5. As the material is removed or abraded from the tooth the block 4| is continually moved toward the pivot 38 until it reaches a positionof slightly greater radius than its final desired position as originally determined. This leaves sufiicient material on the tooth to provide for a final polishing operation. In operation each tooth is ground on one side only and then the index head rotates the ring to the next tooth. After all teeth have been ground on one side, av single lateral adjustment equal to the distance from e to d is made to bring the tool I! at the other center position (see Fig. 1). The same procedure is then followed as for grinding the first faces of the teeth.

The teeth may then be polished in the same manner, a similar sized polishing tool replacing the grinding tool. This method of lapping sprocket teeth provides faces which are particularly smooth, and if any tool marks remain after polishing they will be in the direction of film movement (see Fig. 2) and will not interfere with the separation of the film and teeth during-the progressing of the film by the sprocket.

What is claimed is: y

l. The method of lapping sprocket teeth-with a lapping tool comprising bodily translating said tool over the stationary'faces of said teeth in an arc conforming with'the curvature of the finished faces of said teeth while the instantaneous motion of the abrading surface of said tool with respect to said faces is in a direction from the roots to the tips of the faces of said teeth.

2. The method of lapping the teeth of film driving sprockets with a lapping tool comprising rotating said tool longitudinally of the faces of said sprocket teeth and oscillating said tool in a final are having a radius equal to the radius of the faces of said sprocket teeth plus the radius of said lapping tool.

3. The method of lapping the teeth of film driving sprockets with a grinding tool comprising rotating said tool longitudinally of the faces of said sprocket teeth and oscillating said tool through an are beginning slightly below the base circle of said sprocket teeth and extending to the tips of said sprocket teeth.

4. In a system for lapping sprocket teeth for film driving sprockets, the combination of a lapping tool, means for rotating said tool, means for mounting a sprocket tooth ring in a fixed positlon, pantograph means for oscillating said lapping tool in an arc and means for controlling the gradual diminution of said arc to a final position,

such that it has a radius equal to the sum of the radius of said sprocket tooth and the radius of said grinding tool. I v

5. In a system for lapping the teeth of film driving sprockets comprising a pantograph arrangement, means for mounting a grinding tool on one portion of said pantograph, means for mounting a sprocket tooth ring in a position to be acted upon by said grinding tool, and a pivoted arm connected to another portion of said pantograph for oscillating said tool about said sprocket teeth.

6. In a system for lapping the teeth of motion picture film sprockets comprising a. system of pantograph levers, means for mounting a grinding tool on one of said levers, means for rotating said grinding tool, an index head for holding a sprocket tooth ring in position to be'acted upon by said grinding tool, said grinding tool rotating longitudinally of said sprocket teeth, and a fixed pivoted arm attached to another lever of said pantograph for controlling the movement of said grinding tool about said sprocket teeth.

7. In a system for grinding sprocket teeth for film driving sprockets, the combination of a grinding tool, means for positioning said grinding tool so that its axis of rotation is perpendicular to the plane of said sprocket teeth, pantograph means for oscillating said grinding tool, and means for controlling the arc of oscillation of said tool, the final radius of the arc of oscillation of said tool being slightly greater than the sum of a radius of the face 01' a sprocket tooth and the radius of said grinding tool.

8. The method of lapping sprocket teeth witha lapping tool comprising oscillating said tool whose axis of rotation is perpendicular to the plane of said sprocket teeth, and continually decreasing the oscillating arc of said tool until said are is equal to the sum oi the radius oi a sprocket tooth plus the radius of said tool.

9. In a system for polishing the teeth of motion picture film drive sprockets, the combination of a dividing head. means for mounting a sprocket tooth ring on said head. means for supporting and driving a polishing tool whose axis of rotation is perpendicular to the plane oi said sprocket ring, said supporting means including a pantograph system, means for oscillating said tool about the faces of said sprocket teeth, the center of oscillation of said tool being coincident with the center of curvature of said sprocket tooth faces, said oscillating means including said pantograph system. and means for adjusting said pantograph system to control the arc of oscillation 0! said tool.

' Y ERNEST R088. 

